While for many elderly Americans prescription drugs play a critical role in the management of chronic disease, many face the prospect of receiving inadequate care due to the risk of not being able to afford essential medications. However, very little research has been performed among elderly persons, especially those who are indigent, investigating whether measurement of outpatient prescription medication comprehensiveness may serve as a useful measure of quality of care. We will examine quality of care in elderly Medicare beneficiaries with chronic health conditions in terms of process of care and health care outcomes as a function of comprehensiveness of prescription drug coverage and assess whether the magnitude of the relationship between comprehensiveness of prescription drug coverage and quality of care is greater among indigent subjects. We propose studying elderly Medicare beneficiaries receiving health care at the Group Health Cooperative of the Puget Sound, a large, group model health maintenance organization. Multivariate analyses will use administrative data supplemented with patient survey data, limited chart review, and outside pharmacy data. We will test for relationships between prescription benefit comprehensiveness and process measures including adequacy of and adherence to medication regimen and outcomes including control of blood pressure, blood glucose, and lipids, preventable health care utilization, costs, health status and satisfaction with care. Furthermore, we will examine how results obtained using administrative data alone compare with results from analyses using patient survey, outside pharmacy data, limited chart review, and administrative data. The proposed analyses will provide new information about the relationship between prescription benefit comprehensiveness and quality of care for older Americans and whether knowledge of prescription benefit comprehensiveness may serve as a useful structural quality of care measure. In the current climate of rapidly escalating medication costs yet decreasing numbers of elderly persons with prescription medication coverage, these analyses will help inform the debate around whether to add outpatient prescription benefits to basic Medicare coverage and, if so, how to structure them.